The federal government is partially shut down, and time is running out on the Republican-controlled 115th Congress. It is a dumpster-fire finale for a volatile Republican Congress — a fire set by internal GOP frictions, an impulsive president and ever-more-polarized parties.

The president propelled this year’s third government shutdown over immigration politics. He had promised to sign a stopgap spending bill, even though it wouldn’t fund construction of his campaign promise, a southern border wall. But he changed his mind. The government-stopping reversal followed Trump’s abrupt announcement that, having defeated the Islamic State, he was immediately bringing U.S. troops home from Syria — a decision that prompted bitter opposition from the president’s closest GOP allies and pushed Secretary of Defense Jim Mattis to resign. More fireworks followed on the explosive news that the president was mulling firing Jerome H. Powell, chairman of the Federal Reserve.

The end-of-session chaos bumped two major accomplishments from the headlines: the passage of major criminal justice reforms and a renewal of agricultural programs, which included funding for SNAP, the country’s largest anti-hunger program. But the Republican White House and Congress delivered too little too late for voters, however, who in November had already handed control of the House to the Democrats.

Here are five takeaways from this final year of all-Republican rule.

1. Unified party control doesn’t solve everything

Historically, one-party control of government was powerful: During much of the postwar era, Congress and the president reached policy deals significantly more often when a single party controlled both branches. Think of the enactment of Medicare in 1965 or the Affordable Care Act in 2010.

But the parties began polarizing in the late 1980s, meaning that GOP lawmakers moved further into the conservative camp on the right while Democrats coalesced on the left, making it harder to work across the aisle. And the GOP has fractured ever more contentiously, with factions within the party becoming less willing to compromise. Combined, that means even a nominally unified government has been anything but.

This year, the Republicans divided so profoundly on key issues — especially on immigration — that they proved unable or unwilling to advance the agenda of their nationally unpopular president. And in a polarized era, Democrats paid no price for refusing to bargain.

As a result, none of Trump’s top priorities made it very far, including tough controls on legal and illegal immigration, billions for a southern border wall, big cuts to domestic spending, and major investments to rebuild the nation’s crumbling infrastructure.

Republicans delivered only when they veered to the center — tackling the opioids crisis, improving health care for veterans and children, paring back the Dodd-Frank financial regulations enacted in the wake of the global financial crisis, and busting spending caps on domestic and defense spending alike.

2. One-party rule rarely lasts very long

Trump’s Republican Congress lasted two years. That’s a bit shy of the postwar average: Between 1947 and 2018, unified party government lasted roughly three and a half years.

Why doesn’t unified party government endure? Call it the curse of overreach. Majorities exploit their newfound power to push hard on policy and procedure to advance their agendas. When they inevitably veer off-center to appeal to their base, the public acts as a “thermostat”: When government activism increases, the public demands less, and vice versa.

That pattern typically cuts short party rule. Democrats in 1993-1994 tried to revamp the health-care system and lost control in 1994. Republicans in 2001 pushed hard for tax cuts and lost their majority that spring when then-Sen. James Jeffords of Vermont left the party to become an independent and delivered control of the Senate to the Democrats. Democrats in 2009-2010 overhauled health care, retooled Wall Street and pushed through record fiscal stimulus — and voters punished them in 2010. When Republicans veered to the right in 2017 on health care and tax cuts, voters recoiled and handed power back to the Democrats in 2018.

Over the objections of most Senate Democrats, and after blocking hearings on Obama’s Supreme Court nominee Merrick Garland for nearly a year, Republicans busted the Senate’s filibuster rule in 2017 and confirmed Trump’s nominee Neil M. Gorsuch to the Supreme Court. In 2018, after a bruising and polarizing national debate over sexual misconduct and partisanship, Republicans exploited their new power once more to confirm Justice Brett M. Kavanaugh to the court, this time by one of the slimmest margins in Senate history.

Leaning on the Democrats’ 2013 move that banned filibusters of all other judicial nominees, Senate Republicans in 2018 confirmed 18 appellate and 47 trial judges to the federal bench. Only in a fewcases did Trump’s nominees prove too toxic to GOP senators to confirm.

Still, Senate Republicans refused to heed Trump’s call to nuke the legislative filibuster, which the president thought would have enabled him to secure funding for his border wall. Republicans probably consider the Senate’s supermajority rule a convenient tool for blaming the minority for stalemate — and a protection for years to come, when Democrats again hold the Senate.

4. A fiscal reckoning awaits

During the two years of Republican rule, the national debt grew by $1.9 trillion to reach $21.9 trillion. By the end of 2020, the debt is forecast to rise over $4 trillion more. As a result, the fastest-growing government expense is the interest that the government pays to finance the debt.

Republicans had argued that their 2017 tax cuts would pay for themselves; 2018 data suggest otherwise. This year’s bipartisan deal to raise legal caps on discretionary spending also undermined fiscal discipline. Trump continues to talk about adding a round of middle-class tax cuts, but even his treasury secretary won’t say whether that’s a real proposal. And Congress will hit tough spending caps again next fall, probably generating even more deficit spending.

GOP fiscal hawks who argued for austerity during the Obama presidency appear to have flown away.

5. Will a sleeping Congress awaken?

For much of 2018, the Republican Congress gave Trump a pass. It conducted little oversight of his administration’s controversial policies or personnel. GOP leaders refused to consider measures that would protect special counsel Robert S. Mueller III from Trump’s wrath. Even after the public was outraged by the administration’s highly controversial family-separation policy at the southern border, Republicans refused to hold anyone accountable for the government’s inability to reunite families or for the recent death of a 7-year-old migrant in government custody.

Still, congressional Republicans appear to be awakening. Since this summer they’ve started to challenge the president on his protectionist trade agenda, coziness with authoritarian leaders and unwillingness to condemn Saudi Crown Prince Mohammed bin Salman’s role in the killing of Washington Post contributing columnist Jamal Khashoggi. Most recently, a bipartisan Senate majority voted to order an end to U.S. support for the Saudi war in Yemen. House Democrats could pass a similar resolution next year.

But Republicans will only seriously challenge the president on domestic policy if they decide that’s the only way they’ll be reelected. Tough oversight from Democrats next year, coupled with tightening legal and political vises around Trump, could compel at least some Republicans to reconsider their blind deference to the president, his policies and conduct in office.